First: what is the modification of plastics?

The modification of plastics is to change the original properties of plastics by some physical, chemical and other methods, increase or improve its original properties, and make it more suitable for terminal products.

Second: plastic modification 8 general directions

Which properties of the material have been changed by the general modified plastics? In summary, there are roughly 8 kinds. They are:

1. Density

Changing the density of plastic is divided into two kinds, one is to reduce the density of plastic, and the other is to increase the density of plastic, depending on the choice of terminal application. This article mainly introduces the way to reduce the density of plastics.

Reduce the density of plastic: according to the high school formula M=ρV, that is, when the density of the material is reduced, the quality will also decline with the original product volume, which is commonly used in the lightweight of automobiles and other terminals. Common methods to reduce the density of plastics include adding lightweight fillers or resins, but the density reduction is small. The other is the foaming technology, which has a large weight loss range. But it's a little more difficult.

2. Transparency

Regarding the transparency of plastics, the relationship between crystals and transparency is generally used, the transparency of plastics is related to the crystallinity of products, and its transparency can be improved by controlling the different morphological structures of products.

To measure the transparency of a material, there are many performance indicators that need to be considered. Commonly used indicators are: transmittance, fog, refraction index, birefringence and dispersion. A good transparent material requires the above performance indicators to be excellent and balanced.

Common methods of changing crystal type are:

① Control crystal quality, such as crystal type, spherulite content, crystal size, crystal regularity control.

② Improve the refractive index, mainly by adding high refractive index organic matter or inorganic matter that does not affect the transparency to improve.

③ Reducing birefringence can be achieved by controlling the orientation in the processing, that is, reducing the orientation.

Adding to improve the transparency of plastics refers to the method of adding small molecular substances to transparent resins to improve their transparency. Using this method, the transmittance and refractive index can be improved, and the birefringence can be reduced.

⑤ Adding nucleating agent is the most effective way to increase the light transmittance of transparent resin. Nucleating agent is a small molecule that can promote crystallization. It can play the role of crystal nucleus in the resin, so that the original homogeneous nucleus into heterogeneous nucleation, increase the number of crystal nuclei in the crystallization system, increase the number of microcrystals, reduce the number of spherulites, so that the crystal size is finer, the transparency of the resin is improved.

⑥ Add high refractive index inorganic matter.

⑦ Add substances that can reduce birefringence.

3. Hardness and flexibility

Hardness

Changing the hardness of plastics is divided into surface hardness and overall hardness, generally adding hard additives to plastics, generally rigid inorganic fillers.

Surface hardness: only improve the hardness of the outer surface of plastic products, and the hardness of the internal product is unchanged. The cost is low, mainly used for decorative materials and daily necessities. There are three main methods: coating, coating and surface treatment.

Overall hardness: the general improvement method of plastic blending is to mix high hardness resin in low hardness resin to improve its overall hardness.

Common blend resins are: PS, PMMA, ABS and MF, etc., and the resins that need to be modified are mainly PE, PA, PTFE and PP.

Flexibility

Generally, plasticizers are added to change the flexibility of plastics, and the main role of plasticizers is to improve the processability of resins, that is, to reduce the processing temperature and improve the processing fluidity. However, when added to the relevant resin, it can also give the product flexibility. Suitable for plasticizers to improve flexibility of resins are: PVC, PVDC, CPE, SBS, PA, ABS, PVA and chlorinated polyethers.

4. Processing performance

Improving the processing performance of plastics is generally manifested in: increasing the thermal decomposition temperature of resin. Reduce the melting temperature of resin; Improve the processing flow of resin; Improve the melt properties of resin.

The common modification method is to add modification, add plasticizer and lubricant. Plasticizer can improve polymer plasticity. The function of the lubricant is to reduce the friction between the materials and the surface of the materials and processing equipment, reduce the flow resistance of the melt from the surface, reduce the viscosity of the melt, improve the fluidity of the melt, avoid the adhesion of the melt and the equipment, and improve the surface finish of the product.

5. Strength

Plastics are generally reinforced by adding reinforcing fillers and fibers. Most of the conventional fillers added directly to the resin will cause the tensile strength of the plastic to decrease. However, some directly added special fillers not only do not cause a decline in tensile strength, but will improve the tensile strength to a certain extent, we call such fillers as reinforcing fillers. The reinforcement modification of the reinforcement filling is far less than that of the reinforced fiber, and can only be used in some occasions where the strength requirements are not too high. Plastic fiber reinforcement method is the most commonly used and effective reinforcement method.

Fiber materials for reinforcement are the most important reinforcement materials for plastics, and their dosage can account for more than 90% of the entire reinforcement material. Mainly includes fiber and whisker two categories, the specific varieties are mainly: Inorganic (such as glass fiber, asbestos fiber, carbon fiber, whisker, quartz fiber, graphite fiber and ceramic fiber, etc.), organic (such as PAN fiber, polyethylene fiber, PA fiber, PC fiber, PVC fiber and polyester fiber, etc.), metal (such as boron fiber and aluminum, titanium, calcium and other metal whisker, etc.).

6. Toughness

The toughening of plastics is generally blended with elastomer materials to enhance the toughness of plastics. Commonly used elastomer toughening materials are: high impact resin, such as CPE, MBS, EVA, modified petroleum resin (MPR); High impact rubber, such as ethylene propylene rubber (EPR), ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), styrene butadiene rubber, natural rubber, butyl rubber, neoprene rubber, etc.

7. Thermal performance

The thermal properties affecting the use of plastic products are mainly heat resistance temperature and low temperature. Heat resistance temperature can be mainly expressed as heat deformation temperature, Martin heat resistance temperature and Vica softening point. The low temperature resistance temperature can generally be expressed by embrittlement temperature.

In all fillers, in addition to organic fillers, most inorganic mineral fillers can significantly improve the heat resistance of plastics. Commonly used heat-resistant fillers are: calcium carbonate, talc powder, wollastonite, mica, calcined clay, bauxite and asbestos.

In addition, the enhancement of the plastic changes the heat resistance effect is better than the filling, mainly because the heat resistance of most fibers is very high, and the melting point is mostly more than 1500 degrees Celsius. Commonly used heat resistant fibers are: asbestos fiber, glass fiber, carbon fiber, whisker, polyamide fiber and acrylic fiber.

8. Flame retardant performance

Most plastics are flammable, flame retardant performance is not very good, so in some formulations to add flame retardants, flame retardants are generally able to improve the burning point of plastics, or can inhibit the spread of flame and so on.